The instant invention pertains to sample carrier handling devices, and more particularly, to radiation measuring apparatus using means for mechanically lifting sample carriers from a sample carrier holder to a measuring chamber.
Typically with mechanically operated lifting systems, an elevating rod engages the bottom of the sample carrier in a sample carrier holder, and drives the carrier upward through a vertical tube member into a measuring chamber. When analysis is complete, the elevating rod descends in a direction away from the measuring chamber. Such a system is illustrated in U.S. Pat. No. 3,859,528 (Luitwieler, Jr. et al.). In theory, after the elevating rod ceases to support the sample carrier in a measuring chamber, gravitational force of the sample carrier itself should cause it to descend from the measuring chamber and return to the carrier holder. Because of small clearances between the sample carrier and the vertical tube member, slight irregularities in the shape of the tube member, and static electricity, a sample carrier may remain in its elevated position. When this occurs, a second sample carrier may be elevated beneath the first, causing a malfunction of the instrument. Moreover, malfunctions occur when the gravitational force of the sample carrier is not sufficient to dispel the carrier, resulting in the sample carrier jamming in the vertical tube during its return to the carrier holder.
A solution to this problem is to provide some kind of means to help expel the sample carrier from the vertical tube. U.S. Pat. No. 4,035,642 (Johnson, Jr., et al.) provides such a means, as described in column 3, line 14. "Likewise, to prevent sample carriers from hanging up in the sample zones and to aid in their expulsion, each sample receiving zone is provided with the rods shown in FIG. 1. Holes 33 and 34 are formed in the radiation shield, and alignment with the sample receiving zones 18 and 19. Rods 35 and 36 of suitable length extend through these holes, each rod having a stop 37 and 38 attached to the end of that portion of the rod extending through the radiation shield." Continuing on line 28: "A sample carrier lifted into the sample receiving zone pushes the movable rod vertically up within the zone, while when the sample carrier is being lowered out of the zone, the rod exerts a force down on the carrier, helping to expel it from the zone, the stop limiting the downward motion of the rod within the sample receiving zone."
A significant limitation of sample carrier expulsion means of this type, however, is that the rods extend in a vertical direction beyond the instrument housing. Because the rods extend vertically out of the instrument, placement of the instrument in enclosed confined areas is limited.
An ever present problem with radiation measuring apparatus is contamination. Sample carriers containing a radioactive sample may become contaminated on their external surfaces, and may thus contaminate rods 35 and 36 of Johnson, Jr. et al. upon contact. In this event the rods must be removed from the apparatus and be replaced in entirety, or be decontaminated. This is a result of the rod being one integral unit. It would be desirable to provide means for aiding the expulsion of sample carriers which upon contamination would not have to be decontaminated or replaced in entirety.